CN-122011242-A - Titanium-magnesium catalyst for slurry polymerization process and preparation method thereof

CN122011242ACN 122011242 ACN122011242 ACN 122011242ACN-122011242-A

Abstract

The application discloses a titanium-magnesium catalyst for a slurry polymerization process and a preparation method thereof, belonging to the technical field of olefin polymerization catalysts. The catalyst comprises a composite carrier and a titanium active component loaded on the carrier, wherein the composite carrier is composed of a MgCl 2 matrix and TiO 2 nanofiber, the TiO 2 nanofiber forms a radial through-channel framework inside the carrier, and the crystallinity of the MgCl 2 is distributed in gradient increasing manner from the core of carrier particles to the surface. The preparation method comprises the steps of preparing TiO 2 nanofiber by an alkaline hydrothermal method, dispersing the nanofiber in MgCl 2 ethanol solution, spray drying the nanofiber to form composite particles, gradient heating to construct a crystallinity gradient, calcining at high temperature to crystallize the TiO 2 nanofiber, and loading TiCl 4 . The catalyst of the application is controllably crushed from inside to outside in slurry polymerization, the content of polymer fine powder is effectively reduced, the problem of reactor scaling is greatly solved, and the running period of the device is obviously prolonged.

Inventors

MA LIJUN
ZHANG ZHICHUAN
Bi Fangmin
WEI FENG
WANG WEIWEI

Assignees

淄博新塑化工有限公司

Dates

Publication Date: 20260512
Application Date: 20260415

Claims (10)

1. A titanium-magnesium catalyst for a slurry polymerization process is characterized by comprising a composite carrier with gradient strength distribution and a titanium active component loaded on the carrier, wherein the composite carrier is composed of a MgCl 2 matrix and TiO 2 nano fibers which are distributed in the matrix in a penetrating way, the TiO 2 nano fibers form a radial through-channel framework inside the carrier, the gradient strength distribution is expressed from the core to the surface of carrier particles, and the crystallinity of the MgCl 2 is distributed in a gradient increasing way.
2. The titanium-magnesium catalyst for slurry polymerization process according to claim 1, wherein the diameter of the TiO 2 nanofiber is 10-100nm, the length is 5-50 μm, the length-diameter ratio is more than 50, and the content of the TiO 2 nanofiber in the composite carrier is 5-7wt% of MgCl 2 .
3. The titanium magnesium catalyst for slurry polymerization process according to claim 1, wherein the average particle size of the catalyst is 30-80 μm, the particle size distribution Span value is less than 1.2, the specific surface area is 200-350m 2 /g, the pore volume is 0.4-0.6cm 3 /g, and the gradient difference of crystallinity of MgCl 2 from the core to the surface of the carrier particle is 30-50 percentage points.
4. A method for preparing the titanium magnesium-based catalyst for slurry polymerization process according to any one of claims 1 to 3, characterized by comprising the steps of: (1) Preparing TiO 2 nanofiber by an alkaline hydrothermal method; (2) Dispersing the TiO 2 nanofiber prepared in the step (1) in MgCl 2 ethanol solution, and forming MgCl 2 -EtOH composite particles penetrated by the TiO 2 fiber through spray drying; (3) Carrying out gradient heating dealcoholization treatment on the composite particles in the step (2) to construct gradient distribution of crystallinity of MgCl 2 ; (4) Calcining the product of the step (3) at a high temperature to completely crystallize the TiO 2 fiber; (5) And (3) loading TiCl 4 on the composite carrier in the step (4) to obtain the final catalyst.
5. The method for preparing a titanium magnesium catalyst for slurry polymerization process according to claim 4, wherein the alkaline hydrothermal process in the step (1) is performed under the conditions of NaOH concentration of 8-12mol/L, reaction temperature of 150-200 ℃ and reaction time of 12-36 hours, and the preparation of the TiO 2 nanofiber further comprises the steps of acid exchange and calcination, wherein the acid exchange uses 0.05-0.5mol/LHCl solution, the calcination temperature is 350-500 ℃ and the heat preservation time is 2-5 hours.
6. The method for preparing a titanium magnesium catalyst for slurry polymerization according to claim 4, wherein the amount of the TiO 2 nanofiber added in the step (2) is 1-10wt% of MgCl 2 , and the spray drying conditions are that the air inlet temperature is 140-160 ℃, the air outlet temperature is 80-90 ℃ and the atomization pressure is 0.2-0.3MPa.
7. The method for preparing a titanium magnesium based catalyst for slurry polymerization process according to claim 4, wherein the TiO 2 nanofiber prepared in step (1) is pre-dispersed by a dispersion stabilizer selected from one or more of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, before proceeding to step (2).
8. The method for preparing a titanium magnesium catalyst for slurry polymerization process according to claim 4, wherein the gradient temperature-rising dealcoholization treatment in the step (3) comprises 3 temperature-rising stages, namely, a first stage of 50-70 ℃ for 1-2 hours, a second stage of 80-100 ℃ for 1-2 hours and a third stage of 110-130 ℃ for 2-4 hours, wherein the gradient dealcoholization is carried out in a fluidized bed, the fluidizing medium is inert gas, and the fluidizing gas velocity is 0.2-0.6m/s.
9. The method for preparing a titanium magnesium catalyst for slurry polymerization process according to claim 4, wherein the high temperature calcination temperature in step (4) is 350-450 ℃, the holding time is 2-5 hours, the temperature rising rate is 1-5 ℃ per minute, and the calcination atmosphere is inert gas.
10. A process for preparing a titanium magnesium catalyst for slurry polymerization according to claim 4, wherein the TiCl 4 is supported in the step (5) by a two-step method comprising performing physical adsorption at a low temperature of-20 to 0℃for 1 to 3 hours and then performing chemical bonding at a high temperature of 50 to 100℃for 2 to 5 hours, and the TiCl 4 is supported repeatedly for 1 to 3 times.

Description

Titanium-magnesium catalyst for slurry polymerization process and preparation method thereof Technical Field The application belongs to the technical field of olefin polymerization catalysts, and particularly relates to a titanium-magnesium catalyst for a slurry polymerization process and a preparation method thereof. Background Polyolefins (including polyethylene, polypropylene, etc.) are the largest polymer materials in global yield. Among the numerous processes for producing polyolefins, slurry polymerization processes (also known as slurry polymerization) are dominant. The process uses inert alkane (such as hexane and heptane) as a dispersion medium, so that the generated polymer is suspended in the medium in a form of fine particles, and a homogeneous slurry system is formed by stirring. Titanium-magnesium catalysts are used as a core technology of slurry polymerization processes, anhydrous magnesium chloride is generally used as a carrier, titanium tetrachloride is loaded on the surface or an inner pore canal of the carrier by a chemical or physical method to form a precursor with high activity, and an organic aluminum compound (such as triethylaluminum) is used as a cocatalyst to activate an active center when the catalyst is used. However, with the increasing severity of the downstream market on the performance of polyolefin products and the development of the production process to continuous operation with long period and low cost and high output, the existing catalyst system still faces serious technical challenges in a plurality of key technical links. Among them, the crushing behavior of catalyst particles and the problem of polymer fines generation are one of the key bottlenecks that restrict the long-term stable operation of slurry polymerization units. In the slurry polymerization process, as ethylene monomer continuously diffuses into the pore channels inside the catalyst particles and is intercalated and polymerized on the active center of Ti, polymer chains grow in a limited space of nanometer scale, and huge ingrowth stress is generated. According to high molecular physics analysis, the conformational entropy of the polymer chain in the nanometer limited space is obviously reduced, and the free energy of the system is increased, so that expansion pressure is generated on the pore channel wall surface. When such ingrowth stresses exceed the critical fracture strength of the catalyst support material, cracks will initiate and propagate at the defects of the support. If the strength of the catalyst carrier is too high, the catalyst carrier cannot be crushed controllably and uniformly in the initial stage of polymerization, so that the stress generated by polymer growth cannot be released timely, and the monomer diffusion channel is blocked, whereas if the strength of the catalyst carrier is too low, the catalyst particles can be disintegrated irregularly in a premature and excessive manner under the action of shearing force of polymerization stirring or under the impact of the initial stress of the reaction, so that a large amount of polymer fine powder with the particle size smaller than 44 μm is produced. The fine powder is easy to be adsorbed on the walls of the reaction kettle, the circulating pipeline, the heat exchanger tube bundle and the valve plates of the compressor due to the large specific surface area, high surface energy and obvious surface static effect, and is gradually melted and sintered at high temperature to form flaky or blocky scale, so that the long-period stable operation of the polyolefin device is severely restricted. Various solutions have been proposed in the prior art to address the above-mentioned problems. For example, patent CN1229092a discloses a method of precipitating a solid catalyst by dissolving MgCl 2 in a solvent system to form a uniform solution and then reacting with a titanium compound, but the catalyst particles have a broad particle size distribution and limited fine powder control effect. JP4951379 discloses a preparation method in which anhydrous magnesium chloride is reacted with ethanol to generate MgCl 2·6C2H2 OH alcohol solution, and then reacted with diethylaluminum chloride to precipitate out solid particles, but the particle morphology is poor, and the content of fine powder is high when the preparation method is used for polymerization. CN101942050a discloses a method of adding a halogenated alcohol electron donor compound in the catalyst synthesis process, which can improve the catalyst activity, but has no obvious effect of improving the formation of fine powder. CN117264099a discloses a catalyst system incorporating aluminate compounds, which can obtain a catalyst with a better particle size distribution, but fails to fundamentally solve the problem of controllable breakage of catalyst particles. Therefore, the titanium-magnesium catalyst which can realize the controllable crushing of catalyst particles and obviously reduce the genera